1. Field of the Invention
This invention relates to optics, and more particularly to conversion of a laser beam with an elliptical cross section to a beam with a circular cross section.
2. Description of Related Art
Elliptically shaped (in cross section) light beams output from a laser can be converted into a more desirable circular beam by using a pair of prisms. The output beam from a laser is often in the cross-sectional shape of an ellipse; however, the elliptical shape does not lend itself to optimal performance of associated systems, thereby giving rise to various techniques for converting the elliptical beam into a circular one. Such beam conversion is useful, e.g., in laser beam scanning lithography where a group of parallel laser beams are modulated and scanned over a photosensitive medium to form an image on the medium. Applications are, for instance, in the semiconductor industry for lithography for integrated circuits.
These methods of converting such beam cross sections usually involve transmitting a laser beam through a pair of prisms and then rotating and translating the prisms in relation to each other until the desired cross section was achieved. An incident laser beam is applied to the prism pair, and then an iterative process begins of manipulating the prisms relative to each other. This not only increases post adjustment alignment time for downstream optics, but this also increases the complexity of downstream assemblies due to significant angular and transverse displacement of the output beam relative to the input beam. Therefore, there is a need to be able to quickly adjust an anamorphic prism pair to change the ellipticity of an input laser beam while minimizing angular and transverse beam displacements resulting from the adjustments.
In accordance with the invention, the above problem is overcome by linking an anamorphic pair of prisms, where a first prism simultaneously rotates counter to a second prism, by mechanical linkages. An anamorphic assembly is an optical system providing two different magnifications along two perpendicular axes such as the present assembly where prisms convert an elliptically cross sectioned laser beam into a circularly shaped cross sectioned beam. The prisms are linked such that the first prism translates and rotates simultaneously towards or away from the axis of an input laser beam. Meanwhile, the second prism rotates towards or away from the axis of the input laser beam in a counter-rotating relationship with the first prism. These movements are effected by a single slide adjustment member which translates a slide upon which both prisms are attached.
A first prism mount, upon which the first prism is attached, has a distal end which is attached to the base and a proximal end which is attached to the slide. A second prism mount, upon which the second prism is attached, also has a distal end and a proximal end; however, this distal end is attached to the slide and the proximal end is attached to the base. This arrangement allows the simultaneous adjustment of both prisms using a single slide adjustment member while maintaining the circularity of an output beam cross section over a range of elliptical input beam cross sections. This arrangement also allows for minimizing the angular and transverse displacement of the output beam relative to the input beam.
Furthermore, there is an associated method of simultaneously adjusting a prism pair where a laser beam is input into the entrant face of the first prism, then the slide adjustment member is adjusted. This adjusting rotates and translates the first prism towards or away from the laser beam and rotates the second prism simultaneously towards or away from the laser beam in a fixed counter-rotating manner.